Objective To culture the mouse spermatogonium stem cells(SSCs) then separated and purified,to induce them differentiation EM>in vitro/EM>, and to detect the germ cell nuclear factor (GCNF) expression of mouse SSCs before and after induction. Methods Stem cell factor(SCF) were used to induce spermatogonia to differentiate into the sperma tocytes.The immnofluorescence staining and RT-PCR techniques were uesd in present studies in order to detect GCNF expression before and after differentiation of mouse SSCs. Results SSCs to spermatocytes in mice before and after differentiation were observed by an inverted phase contrast microscope, the cells did not change significantly, they still had a round or oval nucleus that was relatively large; indirect immunofluorescence and RT-PCR results were showed that primary cultured mouse SSCs were GCNF negative, but the 2 days later the spermatocyte (after the induction of differentiation) GCNF began to express. BR> Conclusion The mouse spermatogonium stem cells during the in vitroEM> culture and differentiation process were able to express GCNF./EM>The studies showed that GCNF might be involved in the early differentiation of spermatogonium stem cells. BR>